[#59] Enhance simpleapi/stresstest to also test ydb_subscript_previous_s
[#59] Enhance simpleapi/stresstest to also test ydb_subscript_previous_s

nars1/YottaDBtest,nars1/YottaDBtest,nars1/YottaDBtest,nars1/YottaDBtest,nars1/YottaDBtest,nars1/YottaDBtest